Processes to prepare chlorinated hydrocarbons by the reaction of ethylene, hydrogen chloride and an oxygen-containing gas in the presence of a deacon catalyst are well known and are known in the art as oxychlorination processes. Oxychlorination processes can be carried out in fixed beds as disclosed in British Pat. No. 1,104,666 or fluid beds as disclosed in British Pat. No. 937,985.
The commercial processes usually provide a reaction mixture containing an excess of ethylene and oxygen to insure maximum conversion of hydrogen chloride to chlorinated hydrocarbon. Maximum conversion of hydrogen chloride is desirable since any unconverted hydrogen chloride is separated from the chlorinated hydrocarbons with the water formed in the reaction. The hydrogen chloride is difficult to recover from the water phase and is usually lost as a waste product from the process. In order to insure maximum utilization of the hydrogen chloride, the ethylene and oxygen are usually provided in excess of that stoichiometrically required to react the hydrogen chloride to the desired chlorinated hydrocarbons. Processes which do not provide an excess of ethylene over that requires to react with the hydrogen chloride usually have sufficient unreacted ethylene in the process off-gas to make the recovery of the unreacted ethylene values economically desirable. The unreacted gases which remain after condensation of the water and the chlorinated hydrocarbons formed in the oxychlorination reaction usually contain oxygen, nitrogen, water, small amounts of hydrogen chloride, uncondensed chlorinated hydrocarbons and from about 0.05 to about 25% ethylene. After separating the chlorinated hydrocarbons, water, and hydrogen chloride, the process off-gases can be vented to the atmosphere which adds to atmospheric pollution or burned. The discarding of the ethylene values in the off-gas can present a serious economic loss of ethylene oxychlorination processes.
Processes for recovering the ethylene values from the oxychlorination process off-gas have been developed. Processes such as that disclosed in French Pat. No. 1,421,903 react the ethylene in the wet oxychlorination process off-gas with chlorine, in the vapor phase, at an elevated temperature, in the presence of an iron catalyst, to chlorinate the ethylene in the process off-gas to ethylene dichloride and recover the chlorinated hydrocarbons from the inert and unreacted gases. As used herein ethylene dichloride is used to refer to 1,2-dichloroethane.
Processes of the type which react the ethylene in the wet oxychlorination process off-gas in the vapor phase with chlorine in the presence of a catalyst have two major disadvantages. The processes utilize the gas phase containing relatively large amounts of water vapor. The reaction of ethylene and chlorine in the vapor phase in the presence of a catalyst at an elevated temperature is not selective to ethylene dichloride. Oxygen containing compounds are formed which must be separated from the ethylene dichloride product and can add to the water pollution problems which the process presents. The by-products represent a considerable loss of recoverable ethylene values. Since a substantial amount of water is present during the chlorination, corrosion resistant equipment must be utilized to combat the combined action of water and chlorine. The use of corrosion resistant process equipment presents a significant cost factor in determining the economic feasibility of recovering the ethylene values from ethylene oxychlorination process off-gas.
It is the object of the present invention to provide an improved process for producing ethylene dichloride by the oxychlorination of ethylene. It is an object of the present invention to provide a process in which ethylene values can be economically recovered from oxychlorination process off-gas. It is a further object of the present invention to provide a process which can be accomplished without the need for process equipment fabricated of expensive corrosion resistant materials. It is another object of the present invention to provide a process which is selective to production of ethylene dichloride from ethylene and chlorine and which minimizes the production of oxygenated compounds. It is still a further object of the present invention to provide an improved process which reduces the air pollution potential of ethylene oxychlorination process.